A mixing pipe is already known from DE 20 2007 010 324 U1. The mixing pipe has a cylindrical basic form with a conical enlargement. Nine rows of openings are provided in total, which are each designed as a blade-free recess of the wall. A mixing stage designed in such a way is placed inside the conical enlargement.
A mixing pipe, which is arranged upstream of a funnel element having a perforated lateral surface, is also known from DE 10 2012 010 878 A1.
A two-part mixing pipe, wherein both parts are arranged at a distance from one another and have an at least partially perforated lateral surface, is known from US 2014/0196441 A1.
An exhaust-gas mixer having a mixing pipe is known from EP 2 687 697 A2. The mixing pipe has an exclusively cylindrical basic form. A total of eleven rows of openings are provided, wherein the respective opening is designed as a formation of the wall, and the formed part of the wall at least partially forms a blade. Both the distance of the rows from each other and the distance of the openings in the circumferential direction increase in the direction of flow.